# Full text of "Text Book Of Mechanical Engineering"

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```Appendix III.

939

(4). Loss by ashes and clinker. — This means the heat taken
away when clearing the fires. It can only be reckoned by
weighing the ash and clinker removed, and making a rough
estimate of its temperature. If 4. = temp, of ash and /, that of
stokehole, while '25 is specific heat of ash, we have :

Heat lost
inB.T.U.

-2 5

(5). Loss by unburnt fuel. — In analysing a Ib. of fuel, the
proper percentage of ash will be found. But the ash drawn from
the grate is a greater proportionate amount, and the difference of
the two will be the unburnt carbon, which may be stated per Ib.
of fuel by the heat units it would produce if burnt.

(6). Loss by radiation and other causes is obtained by subtrac-
tion in the balance sheet. It would be more correct to estimate
the radiation and make a separate statement for £ unaccounted/
but this is never done.

(7). Heat used in the evaporation of water.— This is the only
useful application of the heat from the fuel In the first place the
quantity of water used, in Ibs., must be obtained by measuring
the feed supply. The latter is taken from measuring tanks, of
which there should be two, one of which is filling while the other
empties, and a careful noting of the time each tank is started is
all that is required. Water-meters are sometimes used instead of
tanks, but should be carefully tested. The total heat in the steam
may be reckoned from stokehole temperature (p. 597). Then

Heat used
per Ib. of fuel

total heat       ^          total

i ib. of steam j* lbs.jrfdry steam
Ibs. of coal used.

If the steam passing from the boiler be tested by the calori-
meter (p. 878), a small percentage of the total weight will exist as
entrained water (priming water), and this is not useful. Therefore
the total heat in the dry steam and that in the priming water must
be reckoned separately, and the latter will then be put down to
wasteful process, and only the former to useful process. Lastly,
it is usual, outside the balance sheet, to not only state the

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